1. Field of the Invention
The present invention relates to an operation state display apparatus for displaying the operation state of a controlled object.
2. Description of the Prior Art
In a sequence control system which performs a given control operation repeatedly on a regular cycle and in a predetermined order, it has heretofore been extremely difficult to ascertain the position of the machine under control and when and how long and in what order the control elements such as limit switches and solenoid valves have been activated and deactivated. This has made it difficult to service a control system when the controlled object operates abnormally or fails to operate. One approach to this problem is the provision of information on the reference operation and on the operation of the controlled object over a period from the start of one work step, the two informations being available concurrently in a readily visual form. Thus, by comparing these informations with each other, it is possible to expedite the detection of any abnormal machine operation even at such an early stage that the machine appears to be operating normally. Hence, the machine can be stopped before the controlled object is seriously damaged, the cause of abnormality can be easily located, and the machine can be quickly serviced for return to the control line with the result that the machine can be operated with a greater availability and efficiency.